Energy translator



June 1934. D. H. CUNNINGHAM El AL 1,963,191

ENERGY TRANSLATOR Filed July 30, 1930 2 Sheets-Sheet 1 ATTbRNEY June 19, 193 D. H. CUNNINGHAM in AL.

ENERGY TRAN S LATOR Filed July 30, 1930 2 Sheets-Sheet yXwm 7? ATTORNEY Patented June 19, I934 UNiTED STATES PATENT QFFICE' ENERGY TRANSLATOR Application July 30, 1930, Serial No. 471,868

Claims.

t magnetic type whereby improved quality and 0pmonly known as chattering.

cation.

crating efficiency may be obtained.

Our invention, however, will be described with reference to its embodiment in a loud speaker although it should be understood that the principles involved may equally as well be embodied in other energy-translating devices.

Magnetic speakers of the prior art possess certain pronounced characteristics which are usually considered inherent in speakers of that type.

. Tests have shown these speakers to be very inefiicient in the translation of energy from voicefrequency currents into that of the vibrating diaphragm. An abnormal amount of leakage flux and poor correlation of parts were discovered by us to be the chief factors to which this inefficient energy transfer could be attributed. For similar reasons, the power capable of being handled by a speaker of the magnetic type is limited in that the various vibrating elements are permitted, by

' prior known constructions, to shift laterally from their supposedly fixed axis of rotation and, on heavy input currents, the vibrating members are caused to strike neighboring elements of the supporting mechanism, resulting in what is com- Another characteristic defect commonly associated with speakers of the magnetic type is their inability to respond to a wide band of frequencies with a substantially uniform degree of amplifi- In fact, many of the frequencies, especially at either end of the audio-frequency band, are completely absorbed and-do not appear in the output of the loud-speaker mechanism.

We have discovered one cause of the deficiency to be due to the fact that the fundamental frequencies of vibration of certain of the members of the driving mechanism lie within the audiofrequency range and coincide with certain frequencies of the voice currents, thereby producing peak effects in the response curve of the speaker.

Another reason may be attributed to the lateral shifting of elements under the forces transmitted throughout the driving mechanism, whereby high frequencies are usually absorbed and the corresponding energy dissipated before reaching the diaphragm.

The elimination of these defects in a speaker of the magnetic type is not readily conceivable as the problems involved become very complex and intricate.

A speaker of the dynamic type has offered a solution for the difficulties encountered in a speaker of the magnetic type. A speaker of the dynamic type, however, is heavy and bulky and expensive to manufacture. Because of the necessity for a large magnetic field in a speaker of the dynamic type, a constant heavy energy input must be maintained for efiicient operation. Consequently, while the dynamic speaker may have desirable electrical characteristics, it possesses disadvantages because of its cost, its weight and its space requirements.

Broadly speaking, it is one object of .our invention to provide a loud speaker of the magnetic type possessing the advantages of a speaker of the dynamic type.

Another object of our invention is to provide an energy-translating mechanism of the magnetic type having a simple but very efiicient magnetic circuit.

A further object of our invention is to provide an energy-translating mechanism of the magnetic type having an armature so designed and constructed as to respond to high frequencies with substantially the same efficiency as to low frequencies.

A further object of our invention is to provide an energy-translating device having a cone-driverod mechanism so constructed as to pass all desirable frequencies at substantially uniform efliciency.

A further object of our invention is to provide an energy-translating device of the magnetic type having reasonable distribution of mass throughout its driving mechanism.

A further object of our invention is to provide an energy-translating device of the magnetic type having its parts so correlated as to comprise a very simple, light and economical structure capable of producing a substantiall uniform frequency-response curve.

An additional feature of our invention is to provide a'relatively efiicient driving mechanism capable of being combined with a cone diaphragm to form a compact loud speaker having highly desirable characteristics.

An additional feature of our invention resides in a novel means for suspending a cone diaphragm on its supporting frame.

A still further object of our invention is to provide a loud speaker having means for suppressing, to a marked degree, those peaks which might normally occur in the output of the speaker, more particularly, the peak normally occur-3 ring at the lower cut-off frequency. I

Additional features of our invention will be disclosed in the following description, taken in connection with the drawings wherein:

Figure 1* illustrates, in perspective, exploded view, the driving mechanism comprising part of our invention,

Figs. 2 and 3 are detail views of our improved armature construction,

Fig. 4 is a front view of the driving mechanism in assembled relationship, and

Fig. 5 is a sectional view of the driving mechanism, as assembled on the cone-supporting frame.

Fig. 6 is a plan view of the cone and the dampmg means.

Throughout the drawings, like reference numerals designate similar parts.

The objects of our invention are accomplished by means of the structure disclosed in the dra* ings. Referring more particularly to Fig. 1, wherein all the operating elements of the driving mechanism are clearly portrayed, it will be seen that the parts are comparatively few in number and rugged in construction. Various unique features are embodied therein, however, which are not obvious from a casual inspection of the drawings but which will be explicitly pointed out in detail as we proceed with the description of our invention.

The important elements of the driving mechanism, as disclosed in Fig. l, comprise a magnet l, magnetic pole pieces 3 and 5, armature and spring assembly 7, coil 9, armature drive rod 11, cone-drive-rod structure 13, and a frame and support 15 for the coil and the vibrating parts.

Each of these parts, embodying features of our invention, will be considered separately and their cooperation with other elements of our device will be clearly indicated.

Fig. 2 of our drawings discloses, in detail, the construction of our armature and its spring suspension. The problem involved in the design of the armature structure was to obtain a spring suspension for the vibrating element which would be compartively small and simple and which would be responsive to high frequencies. The armature comprises a substantially rectangular element 17 of magnetic material having a small extension 19 at one end to which is secured an armature drive rod 11. The armature is pivotally supported in spaced relationship between a pair of identical punched springs 21 and 23 of phosphor bronze or other, suitable spring material, such as K-monel metal. The pivoting members 25 and 27 are of tapered construction and comprise integral portions of the spring elements struck up therefrom. Slots, provided in the armature along the line of balance, are adapted to receive the tapered ends of the pivots which are wedged therein by means of small rivets 29 and 31, thereby producing a very compact and rugged structure which will function very eiiiciently in responding to the higher frequencies. This method of riveting permits of I the removal of a minimum amount of material from the armature member. Welding may be resorted to in lieu of the riveting method disclosed above. Holes 33, 35, 37 and 39 are provided at extremities of the spring members for mounting purposes.

The armature and spring suspension structure described above possesses the following highly desirable features. The armature is mounted on that end of the tapered pivots where resistance i to torsional twist is a minimum. The base of the pivots, that is, that portion adjacent to th spring members, being of much greater cross sectional area than the tapered ends, will efficiently resist the transmission of the torsional forces in the pivots to the spring members, and, consequently, will cause such forces to be concentrated at the pivot points, whereby the greatest results may be obtained. The armature, therefore, will be free to vibrate at the higher frequencies, as well as the lower ones, as very little, if any, of the energy of the vibrating armature can be transmitted to the supporting springs where it might be consumed in producing a distortion of said spring members.

It will also be noted that any undesirable lateral movement of the armature is effectively opposed by our construction. The spring-suspension means is so constructed as to be capable of resisting great forces in any direction. Consequently, the armature will find its only freedom of mo tion as a vibrating body about an axis which cannot shift, with the result that distortion at this point is avoided.

The above described armature and spring-sup port structure possesses an additional feature in that it permits of the use of a single coil which increases the space factor and contributes toward a more eflicient device; The coil is adapted to snugly fit over the armature springs which exert an outward pressure against the coil and frictionally maintain it in place, thus preventing movement or vibration of the coil transversely of the armature suspension. Means for preventing vibration of the coil in other directions is provided by other elements of the driving mechanism and will be subsequently set forth in the description of such elements.

Referring back to Fig. 1, we have shown a novel cone-drive-rod structure 13 designed for use in combination with our springsuspended-armature construction. This structure comprises a triangular shaped link having a base 41, aside 43 and a hypotenuse 45, the side 43 being longer than the base 41. One end of the hypotenuse, adjacent to the base, is adapted to be soldered or otherwise joined to the armature drive rod 11, a hole 4'? being provided for the purpose, the cone drive rod 49 being attached at the other end of the hypotenuse at right angles to the side. An examination of the drawings will show the armature drive rod and the cone drive rod to be substantially at right angles to each other, thereby changing the direction of force in the armature drive rod through 90 in the direction of the cone drive rod, thus permitting simplification of the magnetic circuit structure, thus allowing it to be supported entirely within the cone structure, as will be more fully described hereinafter.

As stated above, the length of the side of the triangle is greater than that of the base. This ratio of side to base will amplify the distance traveled by the cone, as compared with that of the armature drive rod. Thus, the distance traveled by the cone drive rod per vibration of the armature will be greater than that of the armature drive rod. The mass reactance of tho armature at the high frequencies relative to the cone will decrease through the use of the triangle con struction having arms of unequal length, as described, thus permitting greater motion of the cone at those frequencies. As regards the low frequencies, the apparent compliance of the armature suspension is increased as the ratio of the side to the base is increased and the frequency of resonance of this compliance with the cone mass is lowered, thereby extending the range of low-frequency response. A ratio which we have found very satisfactory is l to the length of the side being approximately one inch and that of the base approximately three-fourths of an inch. The conedrive-rod mechanism is secured at the junction of the base and the side of the triangular portion to a supporting frame 15 by means of a flat flexible steel hinge of considerable width, as compared with that of the members constituting the drive-rod structure. A slit 53, provided adjacent to the junction, imparts additional flexibility to the hinge in the desired direction, and a slot 55, in the edge of the hinge, provides means whereby the drive-rod mechanism may be attached to its supporting frame. The decided width of the hinge will serve to prevent any lateral displacement of the vibrating drive-rod structure outside of its normal plane of vibration.

The hinge disclosed above serves additional purposes in our device, as shown in the drawings. It will be noted that the hinge is so directed as to practically bisect the angle at the point of rotation. Without the hinge located as shown, distortion was found to exist because of the shifting of the center of rotation at inter mediate frequencies from the hinge to points adjacent thereto. By directing the hinge at the angle shown, distortion at the intermediate fre quencies was substantially minimized.

Distortion at high frequencies was also found to be caused by a shifting of the center of rotation in the vibrating members of magnetic speakers from their normal points of rotation. In our device, we have provided a remedy for this undesirable condition by employing a fixed load= ing member '7 at the hinge 51. This results in a concentration of mass at this point about which the inertia of the vibrating structure is comparatively low. At high frequencies, if the center of rotation tends to shift to a new point, the inertia of the vibrating structure will become great about that new point and, in this manner, the loading member will eifectively damp out any tendency of the point of rotation to shift from its normal desired location. At intermediate frequencies, the loading means will function in the same manner but to a less degree and, in so doing, will assist the flexible hinge in performing its function along these lines.

The loading member, as shown, comprises a bar of steel that is materially longer than the width of the vibrating elements and is welded or soldered to the junction of the side and base members, in. which position, it provides a rigid foundation for the wide hinge structure described above.

All the members of the cone-drive-rod mechanism are formed of simple channel-shape steel of comparatively deep channel construction, as is clearly depicted in the drawings, aiding thereby materially in providing a strong rugged structure which is both light in weight and economical to manufacture. The deep-channel-shape design of the members renders them immune to bending stresses likely to occur in speakers of the magnetic type and, in addition, changes the fundamental frequency of undesirable transverse vibration to a frequency which is substantially non-resonant to the band of frequencies in the audible range.

The cone drive rod may be provided with a screw-and-nut connection for attachment to the cone or it may be inserted through the apex of Q the cone and soldered thereto.

The magnetic circuit comprises a permanently magnetized bar 1, preferably of horse-shoe shape, the ends of which are ground on the same plane and are adapted to clamp against a pair of pole pieces 3 and 5, thereby substantially completing a closed metallic magnetic circuit in a single plane. A simplified circuit of this type reduces leakage to a minimum and tends toward a more efiicient operating structure. A magnetic circuit of the type commonly used, having overlapping pole pieces, provides low-reluctance bypass air paths for leakage flux from one pole piece to the magnet end of the opposite polarity. Such conditions are eliminated in our simplified magnetic circuit, thereby producing a corresponding material increase in the efliciency of the speaker.

Additional important features are embodied in our magnetic circuit as illustrated. A comparatively large air gap, of the order of eighteen mils, is provided between the pole pieces. This was found to reduce the percentage of magnetic unbalance for the driver and also to make available large amplitudes of vibration of the armature, which is desirable for low-frequency response. It was also discovered that a highly desirable amplitude-characteristic curve for the vibrating armature could be obtained by providing an armature having a minimum cross sectional area equal to approximately 66% of that of the pole pieces. This particular ratio of armature cross sectional area to pole piece area, in combination with the large air gap referred to above, results in the amplitude of vibration of the armature being substantially proportional to the coil current without the danger of the armature flopping over against the pole pieces.

Milled slots in the opposing faces of the pole pieces result in the formation of a pair of like poles in each pole piece, between which space is provided for the reception of the voice coil. The dimensions of said pole pieces and slots are such as to firmly clamp the coil against movement transversely of the armature. Holes in said pole pieces are provided for mounting purposes.

The armature, the coil, the cone-drive-rod structure and the magnetic circuit are all assembled and mounted on a single die-cast frame or support in a very rugged and compact manner. The coil is fitted into a cutout portion 58 of the support, the two projecting portions 59 and 60 of the support being wedged in between the armature-suspension springs, in which position, the coil and armature assembly is adapted to be secured by means of bolts passing through The cone-drive-rod mechanism 13 is mounted on the armature drive rod 11, the hinged portion 51 being bolted to the support against a surface 69 so arranged that, during non-operating periods, the drive-rod mechanism will be substantially free from internal stresses or strains. A clamping device, comprising a brass plate 70 and a plurality of holding members, is provided for firmly binding the magnet to the pole-piece assembly, as shown. The whole combination, as described. thus results in a reasonable distribution of mass throughout the driving structure.

A supporting frame 71, of drawn steel or other suitable material, is utilized for mounting the driving mechanism described above.

The frame is provided with a plurality of radial arms 73 to' which the driver may be secured. It will be noted that the arms are bent inwardly toward the apex of the cone '15. This construction permits the driver to be located wholly within the space enclosed by the cone speaker, thereby reducing the overall bulk of the speaker. The inturnedarm structure also provides greater resistance to the backward thrusts or reactions of the driving force of the driver, thereby causing the influence of the driving force to be concentrated on the diaphragm, which is highly desirable in any loud speaker.

The cone diaphragm is embossed With a plurality of circular concentric corrugations of such dimensions as to practically eliminate any tendency to set up parasitic vibrations therein, thereby minimizing rattle and permitting the cone to produce the desired characteristics of response. We have found that excellent results are obtained when employing, in combination with our driver, a cone of pulp material constituting the subject matter of application, Serial No. d28,6 l6, (Case #15340), filed February 15, 1980 by R. W. Carlisle et a1. and assigned to the Westinghouse Electrio and Manufacturing Company.

Suspension means for the cone diaphragm is obtained by the use of a special cloth, known in the art as Izarine #1. This particular cloth comprises a rubber-impregnated cotton fabric coated with a cotton nap, forming a very economical and durable weatherproof material, capable of rendering a performance equally as efficient as the relatively expensive soft-leather suspension means heretofore known.

In order to acoustically damp out certain peak effects which might occur in the operation of a cone speaker, particularly, at the low cut-off frequency, we provide a novel means comprising a canopy structure or baflle overlying the major portion of the cone surface and in spaced relation thereto. This canopy consists, preferably, of a perforated cardboard member 79 lined with felt 81, although other suitable materials might be used. Both the cone and the canopy structure are clamped to the driver-supporting frame by means of a split clamping ring which effects a material saving in the cost of manufacture of the speaker, as compared with the use of a complete single-piece ring.

It will thus be seen that the loud speaker described in detail above fulfils the aims and objects of our invention. We have provided a device which is efficient to the maximum degree commensurate with excellent performance, the particular elements of which are so designed, with regard to ruggedness and mass distribution, as to constitute a mechanical filter, whereby the frequency-response range has been widened and the response curve greatly improved over speakers of the prior art.

We have, in addition, provided new and useful improvements in the cone design and suspension, together with cone-damping means which, in combination with our driving mechanism, produce results comparable to that obtained from the more expensive dynamic-type speaker.

While we have described our loud-speaker apparatus in great detail, We do not wish to be limited, in our protection, to the specific details set forth above, except insofar as is necessitated by the prior art and the appended claims.

We claim as our invention:

1. In a sound-translating device, an armature, a support therefor, said support comprising a pair of relatively stifi spring members, pivoting elements struck up therefrom whereby said armature may be suspended from said spring members, said pivoting elements being substantially tapered from said spring members to said armature, whereby said armature may effectively respond to the higher audio frequencies.

2. In a sound-translating mechanism, a driverod construction comprising a triangular shaped link having a base and a side, a relatively stiff flexible hinge member at the junction of said base and side for securing said drive-rod construction to a supporting means, said hinge member being so directed as to substantially coincide With the bisector of the angle formed by said base and side, whereby efficient response at intermediate audio frequencies may be obtained.

3.,As an article of manufacture, a drive-rod structure for a sound-translating device comprising a substantially triangular shaped link having a base and a side, a hinge member secured to said link at the junction of said base and side and so positioned as to substantially coincide with the bisector of the angle formed by said base and side,

said hinge member comprising a relatively thin stiff, flexible element of greater width than the thickness of said link.

4. an article of manufacture, a drive-rod structure for a sound-translating device comprising a substantially triangular shaped link having a base and a side, means at the junction of said base and side for securing said drive-rod structure to a supporting means, and metallic loading means secured to said structure at said junction for obtaining a substantially uniform response at all audio frequencies.

5. As an article of manufacture, a drive-rod structure for sound-translating devices comprising a substantially triangular link having a base and a side, a hinge member at the junction of said base and side comprising a thin flexible element having a width greater than the thickness of said DAVID H. CUNNINGHAM. RICHARD W. CARLISLE. SYDNEY V. PERRY. 

